Research On The Expansion And Shrinkage Characteristics Of Yunnan Red Soil Under Dry-wet Cycles

In this paper,taking the increasingly serious dry and wet circulation of Yunnan laterite,as the research background,taking as Yunnan laterite the research object,the paper put forward the subject of "study on the swelling and shrinkage characteristic of Yunnan laterite under dry and wet cycle".Considering the influence of dry and wet cycle time,dry and wet cycle times,initial dry density,initial water content,load,sample size and other factors,the cyclic expansion and shrinkage characteristics and microstructure characteristics of Yunnan laterite under different factors are studied by the cyclic expansion and shrinkage test,microstructural test and the software image processing method.The expansion and contraction mechanism is of great significance to prevent and control frequent natural disasters in Yunnan.The influence of initial dry density on swelling and shrinkage characteristics of laterite under dry wet cycling is indicated:In the dry and wet cycle,the swelling process of the red soil can be divided into 3 stages,namely,rapid expansion,slow expansion and stable expansion,and the contraction process can be divided into 3 stages: slow contraction,rapid contraction and stable contraction.With the increasing wetting time,the vertical expansion rate,water content and porosity of the laterite were increased with the "factory" type,and the shrinkage parameters such as vertical shrinkage,transverse shrinkage and volume shrinkage were "S",and the water content and porosity decreased gradually with the dehumidification time.With the increase of wetting times,the vertical expansion rate,the lateral expansion rate and the volume expansion rate increased rapidly after the stability,and then decreased slowly.With the increase of dehumidification,the vertical shrinkage rate,the transverse shrinkage rate and the volume shrinkage rate increased first and then then slowly fluctuated.With the increase of the initial dry density,the vertical expansion rate,the vertical shrinkage rate and the volume expansion rate increase,and the lateral expansion rate,the transverse shrinkage rate and the volume shrinkage rate decrease.Vertical expansion is greater than vertical contraction,volume expansion is greater than volume contraction,transverse contraction is greater than vertical contraction.The influence of initial moisture content on swelling and shrinkage characteristics of laterite under dry and wet cycles shows that: With the increase of initial water content,when the swelling and dehumidification are reached,the expansion rate and shrinkage rate are all fluctuating,and the expansion rate and shrinkage rate reach the maximum when the initial water content is 9%.The swelling and shrinkage characteristics of laterite under different loading and size conditions indicate that: Under the same load,the greater the initial dry density,the smaller the total deformation of the red soil under the same load,the greater the initial density,the larger the load,the greater the total deformation of the red soil,and the total deformation of the laterite has nothing to do with the way of loading under the same load.In the same expansion process,the larger the size of the red soil,the greater the initial dry density,the longer the time required for the expansion and contraction stability;the larger the size of the red soil,the greater the initial dry density,the greater the vertical expansion rate,the vertical shrinkage,the lateral expansion rate,the volume expansion rate,the transverse shrinkage rate and the volume shrinkage rate.The smaller the initial water content,the larger the size of the red soil,the larger the vertical expansion rate,the lateral expansion rate and the vertical shrinkage rate,the smaller the volume expansion,the lateral shrinkage and the volume shrinkage,the larger the size of the red soil,the greater the vertical expansion rate,the vertical shrinkage rate,the lateral expansion rate and the body.The smaller the volume expansion rate,the transverse shrinkage rate and the volume shrinkage rate.The microstructure characteristics of the dry and wet cycle show that: After the expansion and stability,the contact of laterite particles is mixed with block and mosaic contact.After the contraction is stable,the clay particles are exposed to the clot and inlaid contact.In the same expansion,the total pore ratio,the roundness of the soil particles and the fractal dimension of the particles increase with the increase of the initial dry density,the degree of orientation and the grain of the particles.The number of particles is reduced.With the increasing number of dry and wet cycles,the total pore ratio of soil and the fractal dimension of particles increase first and then decrease,the roundness of soil particles decreases,and the orientation degree and particle number of particles decrease first and then increase.With the increase of initial water content,after the expansion and stability,the total pore ratio,the roundness of soil particles and the fractal dimension of the particles first decrease and then increase,the orientation of the particles decreases,the number of particles increases first and then decreases.After the contraction,the total pore ratio,the fractal dimension of the particles,the particle number of particles increase,and the particle size increases.The orientation decreases first and then increases.The mechanism of swelling and shrinkage of red soil under dry and wet cycle: The swelling and shrinkage of the laterite is mainly caused by the migration and removal of water.When the water begins to contact with the soil,the water molecules enter the pores in the accumulation body.With the increase of water,the pores in the body are filled with water molecules,and then the space of the aggregates is widened constantly,the volume of the soil is expanded,and the water moves out.In the soil,the pore water in the body gradually escapes and the spacing of the aggregates decreases.When the water content is less than a certain value,the aggregates are broken and moved,and the volume of the soil is contracted in the compact direction.